The present technology generally relates to coating systems and methods suitable for protecting components exposed to high-temperature environments, such as the hostile thermal environment of a turbine engine. More particularly, this technology is directed to an environmental barrier coating (EBC) on a silicon-containing region of a component and to the incorporation of surface features in the silicon-containing region to inhibit creep displacement of the EBC when subjected to shear loading at elevated temperatures.
Higher operating temperatures for turbine engines are continuously sought in order to increase their efficiency. Though significant advances in high temperature capabilities have been achieved through formulation of iron, nickel and cobalt-base superalloys, alternative materials have been investigated. Ceramic composite materials are being developed for such high temperature applications as combustor liners, vanes, shrouds, blades, and other hot section components of turbine engines. Some examples of composite materials include silicon-based composites, for example, composite materials in which silicon, silicon carbide (SiC), silicon nitride (Si3N4), and/or a metal silicide serves as a reinforcement phase and/or a matrix phase.
In many high temperature applications, a protective coating is beneficial or required for a Si-containing material. Such coatings should provide environmental protection by inhibiting the formation of volatile silicon hydroxide (for example, Si(OH)4) products and, desirably, preventing ingress of water vapor to the oxidizing surface. A coating system having these functions will be referred to below as an environmental barrier coating (EBC) system. Desirable properties for the coating material include a coefficient of thermal expansion (CTE) compatible with the Si-containing substrate material, low permeability for oxidants, low thermal conductivity, low silica chemical activity and chemical compatibility with the underlying Si-containing material and thermally grown silica scale.
The silicon content of a silicon-containing bondcoat reacts with oxygen and/or water vapor at high temperatures to form an oxide product, predominantly an amorphous silica (SiO2) scale, though a fraction of the oxide product may be crystalline silica or the (solid or gaseous) oxides of other constituents of the bondcoat. The amorphous silica product exhibits low oxygen permeability. As a result, the silica product that thermally grows on the bondcoat is able to form a protective barrier layer that deters permeation of oxygen into the substrate.